Neutral Tricoordinate Organoboron Derivatives Isoelectronic with Amines and Phosphines

ABSTRACT

Amines and boranes are the archetypical Lewis bases and acids, respectively. The former can readily undergo one-electron oxidation to give radical cations, whereas the latter are easily reduced to afford radical anions. The present invention provides the synthesis of neutral tricoordinate boron derivatives, which act as a Lewis base, and undergoes one-electron oxidation into the corresponding radical cation. The present invention also provides borylene (H—B:) and borinylium (H—B + .) complexes stabilized by two cyclic (alkyl)(amino)carbenes. Ab initio calculations show that the HOMO [Highest Occupied Molecular Orbital] of the borane as well as the SOMO [Singly Occupied Molecular Orbital] of the radical cation are essentially a pair and a single electron in the p(π)-orbital of boron, respectively.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, U.S.Provisional application Ser. No. 61/510,987 filed Jul. 22, 2011, thedisclosure of which is incorporated herein by reference in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant No.CHE0924410, awarded by the National Science Foundation and theDepartment of Defense Grant No. DE-FG02-09ER16069. The Government hascertain rights in this invention.

BACKGROUND OF THE INVENTION

The chemistry of boron is dominated by compounds in which the elementadopts the +3 oxidation state and acts as a potent electron pairacceptor, or Lewis acid. To compensate its intrinsicelectron-deficiency, boron also often participates in multicenter bonds,and numerous clusters involving hypervalent boron centers are known (R.N. Grimes, J. Chem. Educ., 81, 658 (2004)). At the opposite extreme, itis only recently that low-valent boron derivatives have been thoroughlyexplored (D. Vidovic, S. Aldridge, Chem. Sci., 2, 601 (2011); M.Yamashita, K. Nozaki, J. Synth. Org. Chem. Jap., 68, 359 (2010); R. C.Fischer, P. P. Power, Chem. Rev., 110, 3877 (2010); Y. Segawa, M.Yamashita, K. Nozaki, Science, 314, 113 (2006); T. B. Marder, Science,314, 69 (2006); H. Braunschweig, Angew. Chem. Int. Ed., 46, 1946 (2007);K. Nozaki, Nature, 464, 1136 (2010); M. S. Cheung, T. B. Marder, Z. Lin,Organometallics, doi:10.1021/om200115y). Among these species, borylenes(BR), the subvalent boron(I) derivatives analogous to carbenes (CR₂) andnitrenes (NR), have been spectroscopically characterized in solid inertgas matrices at temperatures of a few K (P. Hassanzadeh, L. Andrews, J.Phys. Chem., 97, 4910 (1993); H. F. Bettinger, J. Am. Chem. Soc., 128,2534 (2006)), but to date have eluded preparative isolation.Nonetheless, Braunschweig et al. (H. Braunschweig, C. Kollann, U.Englert, Angew. Chem. Int. Ed., 37, 3179 (1998)) have shown thatborylenes can be incorporated into the ligand sphere of stable andisolable transition metal complexes (H. Braunschweig, R. D. Dewhurst, A.Schneider, Chem. Rev., 110, 3924 (2010)).

In recent years, stable singlet carbenes such as N-heterocyclic carbenes(NHCs) (F. E. Hahn, M. C. Jahnke, Angew. Chem. Int. Ed., 48, 950 (2008);D. Bourissou, O. Guerret, F. P. Gabbaï, G. Bertrand, Chem. Rev., 100, 39(2000)) and cyclic (alkyl)(amino)carbenes (CAACs) (M. Melaimi, M.Soleilhavoup, G. Bertrand, Angew. Chem. Int. Ed., 49, 8810 (2010)) haveproven as powerful as transition metal centers for stabilizing highlyreactive main group element species (Y. Z. Wang, G. H. Robinson, Chem.Commun., 5201 (2009); D. Martin, M. Soleilhavoup, G. Bertrand, Chem.Sci., 2, 389 (2011)). In the boron series, Robinson and co-workers (Y.Wang et al., J. Am. Chem. Soc., 129, 12412 (2007); Y. Wang et al., J.Am. Chem. Soc., 130, 3298 (2008)) have reported that reduction of the(NHC)BBr₃ adduct A produced the isolable stable neutral diborene B,which can be regarded as a dimer of the parent borylene-carbene complex(FIG. 1). Using a similar synthetic approach, Braunschweig andco-workers (P. Bissinger et al., Angew. Chem. Int. Ed., 50, 4704 (2011))have generated the parent borylene-carbene complex D, and although theywere not able to characterize it spectroscopically, trapping experimentsdemonstrated its transient existence.

The extreme reactivity of borylenes is due to their two vacant orbitalsas well as the presence of a lone pair of electrons. As such, there is aneed in the field to which the present invention pertains related to thepreparation, isolation, and use of organoboron derivatives whereinsuitable carbene ligands stabilize a borylene complex. Because CAACs areslightly more nucleophilic, but considerably more electrophilic, thanNHC ligands (V. Lavallo et al., Angew. Chem., Int. Ed., 45, 3488 (2006);0. Back et al., Nature Chem., 2, 369 (2010); G. D. Frey et al., Science,316, 439 (2007)), the present invention surprisingly found that CAACsare useful ligands for stabilizing a borylene complex.

BRIEF SUMMARY OF THE INVENTION

The present invention provides novel organoboron complexes that areisoelectronic with amines and phosphines.

In one aspect, the present invention provides a tricoordinate borylenecomplex, having Formula I:

In Formula I, R¹ and R² are independently alkyl, aryl, arylalkyl,cycloalkyl, cycloalkylalkyl, heteroaryl, heteroarylalkyl,heterocycloalkyl, or heterocycloalkylalkyl. R⁷, R⁸, R⁹, and R¹⁰ areindependently hydrogen, alkyl, aryl, arylalkyl, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, orheterocycloalkylalkyl. At least one of R⁷ and R⁸ is other than hydrogen.At least one of R⁹ and R¹⁰ is other than hydrogen. R³, R⁴, R⁵, R⁶, R¹¹,R¹², R¹³, and a R¹⁴ are independently hydrogen, acyl, alkyl, alkoxy,amino, aryl, arylalkyl cyano, cycloalkyl, cycloalkylalkyl, halo,heteroaryl, heteroarylalkyl, heterocycloalkyl, heterocycloalkylalkyl,hydroxyl, or nitro. R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹²,R¹³, and R¹⁴ are independently optionally substituted with 1-5substituents selected from the group consisting of alkyl, alkoxy, amino,aryl, cycloalkyl, halo, heteroaryl, hydroxyl, and nitro. Also includedare the salts, hydrates, and isomers of Formula I.

In a second aspect, the present invention provides a stable borinyliumradical, having Formula II:

In Formula II, R²¹ and R²² are independently alkyl, aryl, arylalkyl,cycloalkyl, cycloalkylalkyl, heteroaryl, heteroarylalkyl,heterocycloalkyl, or heterocycloalkylalkyl. R²⁷, R²⁸, R²⁹, and R³⁰ areindependently hydrogen, alkyl, aryl, arylalkyl, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, orheterocycloalkylalkyl. At least one of R²⁷ and R²⁸ is other thanhydrogen. At least one of R²⁹ and R³⁰ is other than hydrogen. R²³, R²⁴,R²⁵, R²⁶, R³¹, R³², R³³, and R³⁴ are independently hydrogen, acyl,alkyl, alkoxy, amino, aryl, arylalkyl, cyano, cycloalkyl,cycloalkylalkyl, halo, heteroaryl, heteroarylalkyl, heterocycloalkyl,heterocycloalkylalkyl, hydroxyl, or nitro. R²¹, R²², R²³, R²⁴, R²⁵, R²⁶,R²⁷, R²⁸, R²⁹, R³⁰, R³¹, R³², R³³, and R³⁴ are independently optionallysubstituted with 1-5 substituents selected from the group consisting ofalkyl, alkoxy, amino, aryl, cycloalkyl, halo, heteroaryl, hydroxyl, andnitro. Also included are the hydrates and isomers of Formula II.

In a third aspect, the present invention provides a boronium salt,having Formula III:

In Formula III, R⁶¹ and R⁶² are independently alkyl, aryl, arylalkyl,cycloalkyl, cycloalkylalkyl, heteroaryl, heteroarylalkyl,heterocycloalkyl, or heterocycloalkylalkyl. R⁶⁷, R⁶⁸, R⁶⁹, and R⁷⁰ areindependently hydrogen, alkyl, aryl, arylalkyl, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, orheterocycloalkylalkyl. At least one of R⁶⁷ and R⁶⁸ is other thanhydrogen. At least one of R⁶⁹ and R⁷⁰ is other than hydrogen. R⁶³, R⁶⁴,R⁶⁵, R⁶⁶, R⁷¹, R⁷², R⁷³, and R⁷⁴ are independently hydrogen, acyl,alkyl, alkoxy, amino, aryl, arylalkyl, cyano, cycloalkyl,cycloalkylalkyl, halo, heteroaryl, heteroarylalkyl, heterocycloalkyl,heterocycloalkylalkyl, hydroxyl, or nitro. R⁶¹, R⁶², R⁶³, R⁶⁴, R⁶⁵, R⁶⁶,R⁶⁷, R⁶⁸, R⁶⁹, R⁷⁰, R⁷¹, R⁷², R⁷³, and R⁷⁴ are independently optionallysubstituted with 1-5 substituents selected from the group consisting ofalkyl, alkoxy, amino, aryl, cycloalkyl, halo, heteroaryl, hydroxyl, andnitro. Also included are the hydrates and isomers of Formula III.

In a fourth aspect, the present invention provides a transition metalcomplex including a transition metal and a complex of Formulas I, II, orIII.

In a fifth aspect, the present invention provides a method of preparinga stable tricoordinate boron in the +1 oxidative state by stabilizing aborylene center with a pair of carbene ligands. The methods includescontacting a boron trihalide with a pair of carbene ligands to form acomplex and contacting the complex with KC₈ in toluene.

In a sixth aspect, the present invention provides a tricoordinateborylene complex prepared according to the methods set forth herein.

In a seventh aspect, the present invention provides a method ofcatalyzing a reaction including combining a reactant with the transitionmetal complex as set forth herein under conditions sufficient forcatalysis to occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. (Top) Synthesis of the neutral bis(carbene)-stabilized diboreneB, the dimer of the parent borylene-NHC adduct, by Robinson andcoworkers (Y. Wang et al., J. Am. Chem. Soc., 129, 12412 (2007); Y. Wanget al., J. Am. Chem. Soc., 130, 3298 (2008)) (Dipp:2,6-diisopropylphenyl). (Bottom) Generation of a transient parentborylene-NHC adduct D by Braunschweig and coworkers (P. Bissinger etal., Angew. Chem. Int. Ed., 50, 4704 (2011)) (Np: Naphthalene).

FIG. 2. Synthesis of the parent borylene-bis(CAAC) adduct 3 representedunder two canonical forms, its oxidation with gallium trichloride to thestable radical cation 3⁺, and its protonation withtrifluoromethanesulfonic acid to afford the boronium salt [3H⁺]CF₃SO₃—(Dipp: 2,6-diisopropylphenyl).

FIG. 3. Molecular views (50% thermal ellipsoids are shown) of the parentborylene-bis(CAAC) 3 (left), radical cation 3⁺. (center), and boronium3H⁺ (right) in the solid state (for clarity H atoms of the carbeneligand and the counterions GaCl₄ ⁻ for 3⁺ and CF₃SO₃ ⁻ for 3H⁺ areomitted. Selected bond lengths (Å) and angles (°) are given in theTable; for comparison, the calculated values at the (U)BP86/def2-SVPlevel of theory are given in brackets.

FIG. 4. Plot of the calculated highest-lying occupied molecular orbital(HOMO) (−3.34 eV) of the parent borylene-bis(CAAC) 3 (left), and singlyoccupied molecular orbital (SOMO) (−7.30 eV) of the radical cation 3⁺(right).

FIG. 5. The FTIR spectrum of 3 in the solid state.

FIG. 6. The Cyclic voltammogram of a THE solution of 3 (01 M nBu₄NPF₆ aselectrolyte, scan rate 100 mVs⁻¹, potential versus Fc⁺/Fc).

FIG. 7. Experimental EPR spectrum (9.3305 GHz) of [3⁺.]GaCl₄ ⁻ in THF at298 K (top), and the computer simulation with Win Sim 2002 program(bottom).

FIG. 8. Schematic representation of the donor-acceptor bonding in thecompound 3.

FIG. 9. Plot of the frontier orbitals of 3 and 3⁺. The eigenvalues (eV)are calculated at (U)BP86/def2-SVP.

FIG. 10. The Spin density and the NBO (45) charges of the radical cation3⁺. at UBP86/def2-SVP.

DETAILED DESCRIPTION OF THE INVENTION I. General

The present invention provides organoboron complexes and derivatives,including neutral tricoordinate boron derivatives, as well as methods ofmaking the same, which act as Lewis bases and undergoes one-electronoxidation into corresponding radical cations. The present invention alsoprovides borylene (H—B:) and borinylium (H—B⁺.) complexes stabilized bytwo cyclic (alkyl)(amino)carbenes as well as methods of making the same.The present invention demonstrates that neutral tricoordinateorganoboron, featuring boron in the +1 oxidation state, can be oxidizedto afford the corresponding stable radical cation, and also protonatedto give the conjugate acid.

II. Definitions

The abbreviations used herein have their conventional meaning within thechemical and biological arts.

Where substituent groups are specified by their conventional chemicalformulae, written from left to right, they equally encompass thechemically identical substituents that would result from writing thestructure from right to left, e.g., —CH₂O— is equivalent to —OCH₂—.

As used herein, the term “alkyl” refers to a straight or branched,saturated, aliphatic radical having one to six carbon atoms, unlessotherwise indicated (e.g., alkyl includes methyl, ethyl, propyl,isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, and the like).

Alkyl represented along with another radical (e.g., as in arylalkyl;heteroarylalkyl; cycloalkylalkyl; or heterocycloalkylalkyl) means astraight or branched, saturated aliphatic divalent radical having thenumber of atoms indicated (e.g., aralkyl includes benzyl, phenethyl,1-phenylethyl 3-phenylpropyl, and the like). It should be understoodthat any combination term using an “alk” or “alkyl” prefix refers toanalogs according to the above definition of “alkyl”. For example, termssuch as “alkoxy” “alkylhio” refer to alkyl groups linked to a secondgroup via an oxygen or sulfur atom.

As used herein, the term “alkylene” refers to either a straight chain orbranched alkylene of 1 to 7 carbon atoms, i.e. a divalent hydrocarbonradical of 1 to 7 carbon atoms; for instance, straight chain alkylenebeing the bivalent radical of Formula —(CH₂)_(n)—, where n is 1, 2, 3,4, 5, 6 or 7. Preferably alkylene represents straight chain alkylene of1 to 4 carbon atoms, e.g. a methylene, ethylene, propylene or butylenechain, or the methylene, ethylene, propylene or butylene chainmono-substituted by C₁-C₃-alkyl (preferably methyl) or disubstituted onthe same or different carbon atoms by C₁-C₃-alkyl (preferably methyl),the total number of carbon atoms being up to and including 7. One ofskill in the art will appreciate that a single carbon of the alkylenecan be divalent, such as in —(HC(CH₂)_(n)CH₃)—, wherein n=0-5.

As used herein, the term “alkoxy” refers to a radical —OR where R is analkyl group as defined above e.g., methoxy, ethoxy, and the like.

As used herein, the term “amino” means the radical —NH₂. Unlessindicated otherwise, the compounds of the invention containing aminomoieties include protected derivatives thereof. Suitable protectinggroups for amino moieties include acetyl, tert-butoxycarbonyl,benzyloxycarbonyl, and the like.

As used herein, the term “aryl” refers to a monocyclic or fusedbicyclic, tricyclic or greater, aromatic ring assembly containing 6 to16 ring carbon atoms. For example, aryl may be phenyl, benzyl ornaphthyl, preferably phenyl. “Arylene” means a divalent radical derivedfrom an aryl group. Aryl groups can be mono, di, or tri substituted byone, two or three radicals selected from alkyl, alkoxy, aryl, hydroxy,halogen, cyano, amino, amino alkyl, trifluoromethyl, alkylenedioxy andoxy C₂-C₃ alkylene, or 1 or 2 naphthyl; or 1 or 2 phenanthrenyl.

As used herein, the term “aralkyl” means a radical -(alkylene)-R where Ris aryl as defined above e.g., benzyl, phenethyl, and the like.

As used herein, the term “cycloalkyl” refers to a saturated or partiallyunsaturated, monocyclic, fused bicyclic or bridged polycyclic ringassembly containing from 3 to 12 ring atoms, or the number of atomsindicated. For example, C₃-C₈ cycloalkyl includes cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.Cycloalkyl also includes norbornyl and adamantyl.

As used herein, the term “cycloalkylalkyl” means a radical -(alkylene)-Rwhere R is cycloalkyl as defined above.

As used herein, the term “cyclic (alkyl)(amino)carbene” refers to acarbene having a cycloalkyl group and an amino group bonded together,e.g., the cyclic (alkyl)(amino)carbene may include

The amino group may be in a straight chain or as a cyclic group such asa heterocyclic carbene or an N-heterocyclic carbene. Example cyclic(alkyl)(amino)carbenes (CAACs) are set forth in M. Melaimi, M.Soleilhavoup, G. Bertrand, Angew. Chem. Int. Ed., 49, 8810. (2010))

As used herein, the terms “halo” or “halogen,” by themselves or as partof another substituent, mean, unless otherwise stated, a fluorine,chlorine, bromine, or iodine atom.

As used herein, the terms “heterocycloalkyl” and “heterocyclic” refer toa ring system having from 3 ring members to about 20 ring members andfrom 1 to about 5 heteroatoms such as N, O and S. For example,heterocycle includes, but is not limited to, tetrahydrofuranyl,tetrahydrothiophenyl, morpholino, pyrrolidinyl, pyrrolinyl,imidazolidinyl, imidazolinyl, pyrazolidinyl, pyrazolinyl, piperazinyl,piperidinyl, indolinyl, quinuclidinyl and1,4-dioxa-8-aza-spiro[4.5]dec-8-yl.

As used herein, the term “heterocycloalkylalkyl” means a radical-(alkylene)-R where R is heterocycloalkyl as defined above.

As used herein, the term “heteroaryl” refers to a monocyclic or fusedbicyclic or tricyclic aromatic ring assembly containing 5 to 16 ringatoms, where from 1 to 4 of the ring atoms are a heteroatom each N, O orS. For example, heteroaryl includes pyridyl, indolyl, indazolyl,quinoxalinyl, quinolinyl, isoquinolinyl, benzothienyl, benzofuranyl,furanyl, pyrrolyl, thiazolyl, benzothiazolyl, oxazolyl, isoxazolyl,triazolyl, tetrazolyl, pyrazolyl, imidazolyl, thienyl, or any otherradicals substituted, especially mono or di substituted, by e.g. alkyl,nitro or halogen. Pyridyl represents 2, 3, or 4 pyridyl, advantageously2 or 3 pyridyl. Thienyl represents 2 or 3 thienyl. Quinolinyl representspreferably 2, 3, or 4 quinolinyl. Isoquinolinyl represents preferably 1,3, or 4 isoquinolinyl. Benzopyranyl, benzothiopyranyl representspreferably 3 benzopyranyl or 3 benzothiopyranyl, respectively. Thiazolylrepresents preferably 2 or 4 thiazolyl, and most preferred, 4 thiazolyl.Triazolyl is preferably 1, 2, or 5 (1,2,4 triazolyl). Tetrazolyl ispreferably 5 tetrazolyl.

As used herein, the term “heteroaralkyl” means a radical -(alkylene)-Rwhere R is heteroaryl as defined above.

Preferably, heteroaryl is pyridyl, indolyl, quinolinyl, pyrrolyl,thiazolyl, isoxazolyl, triazolyl, tetrazolyl, pyrazolyl, imidazolyl,thienyl, furanyl, benzothiazolyl, benzofuranyl, isoquinolinyl,benzothienyl, oxazolyl, indazolyl, or any of the radicals substituted,especially mono or di substituted.

Substituents for the aryl and heteroaryl groups are varied and areselected from: halogen, OR′, OC(O)R′, NR′R″, SR′, R′, CN, NO₂, CO₂R′,CONR′R″, C(O)R′, OC(O)NR′R″, NR″C(O)R′, NR″C(O)₂R′, NR′C(O)NR″R″′, NHC(NH₂)═NH, NR′C(NH₂)═NH, NH C(NH₂)═NR′, S(O)R′, S(O)₂R′, S(O)₂NR′R″, N₃,CH(Ph)₂, perfluoro(C₁-C₄)alkoxy, and perfluoro(C₁-C₄)alkyl, in a numberranging from zero to the total number of open valences on the aromaticring system; and where R′, R″ and R′″ are independently selected fromhydrogen, C₁-C₈alkyl and heteroalkyl, unsubstituted aryl and heteroaryl,(unsubstituted aryl) (C₁-C₄)alkyl, and (unsubstituted aryl)oxy(C₁-C₄)alkyl.

As used herein, the term “hydroxyl” refers to the radical having theformula OH.

Each of the above terms (e.g., “alkyl,” “heteroalkyl,” “aryl” and“heteroaryl”), when indicated as “substituted” or “optionallysubstituted,” are meant to include both substituted and unsubstitutedforms of the indicated radical.

Substituents for the alkyl and heteroalkyl radicals (including thosegroups often referred to as alkylene, alkenyl, heteroalkylene,heteroalkenyl, alkynyl, cycloalkyl, heterocycloalkyl, cycloalkenyl, andheterocycloalkenyl) can be one or more of a variety of groups selectedfrom, but not limited to: —OR′, ═O, ═NR′, ═N—OR′, —NR′R″, —SR′,-halogen, —SiR′R″R′″, —OC(O)R′, —C(O)R′, —CO₂R′, —CONR′R″, —OC(O)NR′R″,—NR″C(O)R′, —NR′—C(O)NR″R′″, —NR″C(O)₂R′, —NR—C(NR′R″R′″)═NR″,—NR—C(NR′R″)═NR′″, —S(O)R′, —S(O)₂R′, —S(O)₂NR′R″, —NR(SO₂)R′, —CN and—NO₂ in a number ranging from zero to (2m′+1), where m′ is the totalnumber of carbon atoms in such radical. R′, R″, R′″ and R′″ are eachindependently selected from hydrogen, C₁-C₈ alkyl and heteroalkyl,unsubstituted aryl and heteroaryl, (unsubstituted aryl)-(C₁-C₄)alkyl,and (unsubstituted aryl)oxy-(C₁-C₄)alkyl. When a compound of theinvention includes more than one R group, for example, each of the Rgroups is independently selected as are each R′, R″, R′″ and R″″ groupswhen more than one of these groups is present. When R′ and R″ areattached to the same nitrogen atom, they can be combined with thenitrogen atom to form a 4-, 5-, 6-, or 7-membered ring. For example,—NR′R″ is meant to include, but not be limited to, 1-pyrrolidinyl and4-morpholinyl. From the above discussion of substituents, one of skillin the art will understand that the term “substituted alkyl” is meant toinclude groups including carbon atoms bound to groups other thanhydrogen groups, such as haloalkyl (e.g., —CF₃ and —CH₂CF₃) and acyl(e.g., —C(O)CH₃, —C(O)CF₃, —C(O)CH₂OCH₃, and the like).

As used herein, the term “i-Pr” refers to isopropyl, e.g.,

As used herein, the term “KC₈” refers to potassium graphite.

As used herein, the term “salt” refers to acid or base salts of thecompounds used in a method of the present invention. Illustrativeexamples of acceptable salts are mineral acid (hydrochloric acid,hydrobromic acid, phosphoric acid, and the like) salts, organic acid(acetic acid, propionic acid, glutamic acid, trifluoroacetic acid,trifluoromethanesulfonic acid, citric acid and the like) salts,quaternary ammonium (methyl iodide, ethyl iodide, and the like) salts.

As used herein, the term “isomers” refers to compounds having the samenumber and kind of atoms, and hence the same molecular weight, butdiffering in respect to the structural arrangement or configuration ofthe atoms.

As used herein, the terms “a,” “an,” or “a(n)”, when used in referenceto a group of substituents or “substituent group” herein, mean at leastone. For example, where a compound is substituted with “an” alkyl oraryl, the compound is optionally substituted with at least one alkyland/or at least one aryl, wherein each alkyl and/or aryl is optionallydifferent. In another example, where a compound is substituted with “a”substituent group, the compound is substituted with at least onesubstituent group, wherein each substituent group is optionallydifferent.

Description of compounds of the present invention are limited byprinciples of chemical bonding known to those skilled in the art.Accordingly, where a group may be substituted by one or more of a numberof substituents, such substitutions are selected so as to comply withprinciples of chemical bonding and to give compounds which are notinherently unstable and/or would be known to one of ordinary skill inthe art as likely to be unstable under ambient conditions, such asaqueous, or neutral conditions.

III. Compounds and Complexes

In one embodiment, the present invention provides a tricoordinateborylene complex, having the structure of Formula I:

In Formula I, R¹ and R² are independently alkyl, aryl, arylalkyl,cycloalkyl, cycloalkylalkyl, heteroaryl, heteroarylalkyl,heterocycloalkyl, or heterocycloalkylalkyl. R⁷, R⁸, R⁹, and R¹⁰ areindependently hydrogen, alkyl, aryl, arylalkyl, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, orheterocycloalkylalkyl. At least one of R⁷ and R⁸ is other than hydrogen.At least one of R⁹ and R¹⁰ is other than hydrogen. R³, R⁴, R⁵, R⁶, R¹¹,R¹², R¹³, and R¹⁴ are independently hydrogen, acyl, alkyl, alkoxy,amino, aryl, arylalkyl cyano, cycloalkyl, cycloalkylalkyl, halo,heteroaryl, heteroarylalkyl, heterocycloalkyl, heterocycloalkylalkyl,hydroxyl, or nitro. R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹²,R¹³, and R¹⁴ are independently optionally substituted with 1-5substituents selected from the group consisting of alkyl, alkoxy, amino,aryl, cycloalkyl, halo, heteroaryl, hydroxyl, and nitro. Also includedare the salts, hydrates, and isomers thereof.

In some embodiments, the complex has the following structure:

Y¹, Y², Y³, and Y⁴ are independently aryl, arylalkyl, cycloalkyl, orcycloalkylalkyl. Y¹, Y², Y³, and Y⁴ are independently optionallysubstituted with from 1-5 substituents selected from the groupconsisting of alkyl, aryl, halo, heteroaryl, and hydroxyl. In someembodiments, Y¹ or Y² is aryl or optionally both Y¹ and Y² are aryl. Insome embodiments, Y¹ or Y² is 2,6-diisopropyl-phenyl or optionally bothY¹ and Y² are 2,6-diisopropyl-phenyl. In some other embodiments, Y³ orY⁴ is cycloalkyl or optionally both Y³ and Y⁴ are cycloalkyl. In certainembodiments, Y³ or Y⁴ is cyclohexyl or optionally both Y³ and Y⁴ arecyclohexyl.

In some embodiments, the complex has the following structure:

R¹⁵, R¹⁶, R¹⁷, R¹⁸, R¹⁹, R²⁰, R²¹, R²², R²³, and R²⁴ are independentlyhydrogen, acyl, alkyl, alkoxy, amino, cyano, halo, or nitro. In someembodiments, R¹⁵, R¹⁶, R²⁰, and R²⁴ are isopropyl.

In some of these embodiments, Y³ and Y⁴ are cyclohexyl.

In some embodiments, the complex has the following structure:

As used herein, i-Pr refers to isopropyl.

In other embodiments, the complex has the following structure:

In still other embodiments, the complex has the following structure:

In other embodiments, the complex has the following structure:

In other embodiments, the complex has the following resonance structure:

In some other embodiments, the present invention provides a stableborinylium radical having the structure of Formula II:

In Formula II, R²¹ and R²² are independently alkyl, aryl, arylalkyl,cycloalkyl, cycloalkylalkyl, heteroaryl, heteroarylalkyl,heterocycloalkyl, or heterocycloalkylalkyl. R²⁷, R²⁸, R²⁹, and R³⁰ areindependently hydrogen, alkyl, aryl, arylalkyl, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, orheterocycloalkylalkyl. At least one of R²⁷ and R²⁸ is other thanhydrogen. At least one of R²⁹ and R³⁰ is other than hydrogen. R²³, R²⁴,R²⁵, R²⁶, R³¹, R³², R³³, and R³⁴ are independently hydrogen, acyl,alkyl, alkoxy, amino, aryl, arylalkyl, cyano, cycloalkyl,cycloalkylalkyl, halo, heteroaryl, heteroarylalkyl, heterocycloalkyl,R²², R²³, R²⁴, R²⁵, R²⁶, R²⁷, R²⁸, R²⁹, R³⁰, R³¹, R³²,heterocycloalkylalkyl, hydroxyl, or nitro. R²¹, R³³, and R³⁴ areindependently optionally substituted with 1-5 substituents selected fromthe group consisting of alkyl, alkoxy, amino, aryl, cycloalkyl, halo,heteroaryl, hydroxyl, and nitro. Also included are the hydrates orisomers of Formula II. In certain embodiments, the GaCl₄ ⁻ issubstituted for another suitable anion.

In some embodiments, the radical has the following structure:

Y²¹, Y²², Y²³, and Y²⁴ are independently aryl, arylalkyl, cycloalkyl, orcycloalkylalkyl. Y²¹, Y²², Y²³, and Y²⁴ are independently optionallysubstituted with from 1-5 substituents selected from the groupconsisting of alkyl, aryl, halo, heteroaryl, and hydroxyl.

In certain embodiments, the radical has the following structure:

R⁴⁵, R⁴⁶, R⁴⁷, R⁴⁸, R⁴⁹, R⁵⁰, R⁵¹, R⁵², R⁵³, and R⁵⁴ are independentlyhydrogen, halo, acyl, alkyl, alkoxy, amino, cyano, or nitro.

In some embodiments, the radical has the following structure:

In other embodiments, the radical has the following structure:

In other embodiments, the radical has the following structure:

In some other embodiments, the radical has the following structure:

In other embodiments, the radical has the following resonance structure:

In certain embodiments, the present invention provides a boronium salt,having the structure of Formula III:

In Formula III, R⁶¹ and R⁶² are independently alkyl, aryl, arylalkyl,cycloalkyl, cycloalkylalkyl, heteroaryl, heteroarylalkyl,heterocycloalkyl, or heterocycloalkylalkyl. R⁶⁷, R⁶⁸, R⁶⁹, and R⁷⁰ areindependently hydrogen, alkyl, aryl, arylalkyl, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, orheterocycloalkylalkyl. At least one of R⁶⁷ and R⁶⁸ is other thanhydrogen. At least one of R⁶⁹ and R⁷⁰ is other than hydrogen. R⁶³, R⁶⁴,R⁶⁵, R⁶⁶, R⁷¹, R⁷², R⁷³, and R⁷⁴ are independently hydrogen, acyl,alkyl, alkoxy, amino, aryl, arylalkyl, cyano, cycloalkyl,cycloalkylalkyl, halo, heteroaryl, heteroarylalkyl, heterocycloalkyl,heterocycloalkylalkyl, hydroxyl, or nitro. R⁶¹, R⁶², R⁶³, R⁶⁴, R⁶⁵, R⁶⁶,R⁶⁷, R⁶⁸, R⁶⁹, R⁷⁰, R⁷¹, R⁷², R⁷³, and R⁷⁴ are independently optionallysubstituted with 1-5 substituents selected from the group consisting ofalkyl, alkoxy, amino, aryl, cycloalkyl, halo, heteroaryl, hydroxyl, andnitro. Also included are the hydrates and isomers of Formula III. Inother embodiments, the CF₃SO₃ ⁻ is substituted for another suitableanion.

In other embodiments, the salt has the following structure:

Y³¹, Y³², Y³³, and Y³⁴ are independently aryl, arylalkyl, cycloalkyl, orcycloalkylyl. Y³¹, Y³², Y³³, and Y³⁴ are independently optionallysubstituted with from 1-5 substituents selected from the groupconsisting of alkyl, aryl, halo, heteroaryl, and hydroxyl.

In other embodiments, the salt has the following structure:

R⁸⁵, R⁸⁶, R⁸⁷, R⁸⁸, R⁸⁹, R⁹⁰, R⁹¹, R⁹², R⁹³, and R⁹⁴ are independentlyselected from the group consisting of hydrogen, halo, acyl, alkyl,alkoxy, amino, cyano, and nitro.

In other embodiments, the salt has the following structure:

In some other embodiments, the salt has the following structure:

In certain embodiments, the salt has the following structure:

In other embodiments, the salt has the following structure:

In certain other embodiments, the salt has the following resonancestructure:

IV. Transition Metal Complexes

In other embodiments, the present invention provides a transition metalcomplex comprising a transition metal and a compound or complex ofFormulas I, II, or III. In some embodiments, a compound or complex ofFormulas I, II, or III is a tricoordinate boron, as set forth herein,wherein the boron is in the +1 oxidative state and is isoelectronic withan amine. In other embodiments, the present invention provides atransition metal complex, wherein the tricoordinate boron is in the +1oxidative state and is substantially as provided in FIG. 2.

In some embodiments, the present invention provides metal complexes,including at least one ligand selected from Formulas I, II, or III thatare useful as catalysts in a variety of organic reactions. One of skillin the art will appreciate that such complexes can employ a number ofmetals, including, but not limited to, transition metals, and have avariety of geometries (e.g., trigonal, square planar, trigonalbipyramidal and the like) depending on the nature of the metal and itsoxidation state and other factors including, for example, additionalligands.

In some other embodiments, the present invention provides a coordinationcomplex including a metal atom and at least one ligand selected fromFormulas I, II, or III.

In some embodiments, the present invention provides a coordinationcomplex including a metal atom and at least one ligand selected fromFormulas I, II, or III, wherein the metal atom is selected from Li, Na,K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr,Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn,Cd, Hg, Al, Ga, In, Tl, Ge, Sn, Pb, Sb, Bi, or Po. In some embodiments,the metal atom is selected from Ir, Pd, Rh Ru, or Au. In some otherembodiments, the coordination complex further includes at least oneligand selected from halide, pseudohalide, tetraphenylborate,perhalogenated tetraphenylborate, tetrahaloborate, hexahalophosphate,hexahaloantimonate, trihalomethanesulfonate, alkoxide, carboxylate,tetrahaloaluminate, tetracarbonylcobaltate, hexahaloferrate(III),tetrahaloferrate(III), tetrahalopalladate(II), alkylsulfonate,arylsulfonate, perchlorate, cyanide, thiocyanate, cyanate, isocyanate,isothiocyanate, amines, imines, phosphines, phosphites, carbonylcompounds, alkenyl compounds, allyl compounds, carboxyl compounds,nitriles, alcohols, ethers, thiols or thioethers. In some embodiments,the coordination complex includes gold; a complex having Formulas I, II,or III; and optionally a member selected from bent-allenes, phosphines,sulfonated phosphines, phosphites, phosphinites, phosphonites, arsines,stibines, ethers, ammonia, amines, amides, sulfoxides, carbonyls,nitrosyls, pyridines and thioethers.

In general, any transition metal (e.g., a metal having d electrons) canbe used to form the complexes/catalysts of the present invention. Forexample, suitable transition metals are those selected from one ofGroups 3-12 of the periodic table or from the lanthanide series.Preferably, the metal will be selected from Groups 5-12 and even morepreferably Groups 7-11. For example, suitable metals include platinum,palladium, iron, nickel, iridium, ruthenium and rhodium. The particularform of the metal to be used in the reaction is selected to provide,under the reaction conditions, metal centers which are coordinatelyunsaturated and not in their highest oxidation state.

To further illustrate, suitable transition metal complexes and catalystsinclude soluble or insoluble complexes of platinum, palladium, iridium,iron, rhodium, ruthenium and nickel. Palladium, rhodium, iridium,ruthenium and nickel are particularly preferred and palladium is mostpreferred.

The transition metal complexes of the present invention can includeadditional ligands as required to obtain a stable complex. Theadditional ligands can be neutral ligands, anionic ligands and/orelectron-donating ligands. The ligand can be added to the reactionmixture in the form of a metal complex, or added as a separate reagentrelative to the addition of the metal.

Anionic ligands suitable as additional ligands are preferably halide,pseudohalide, tetraphenylborate, perhalogenated tetraphenylborate,tetrahaloborate, hexahalophosphate, hexahaloantimonate,trihalomethanesulfonate, alkoxide, carboxylate, tetrahaloaluminate,tetracarbonylcobaltate, hexahaloferrate(III), tetrahaloferrate(III)or/and tetrahalopalladate(II). Preferably, an anionic ligand is selectedfrom halide, pseudohalide, tetraphenylborate, perfluorinatedtetraphenylborate, tetrafluoroborate, hexafluorophosphate,hexafluoroantimonate, trifluoromethanesulfonate, alkoxide, carboxylate,tetrachloroaluminate, tetracarbonylcobaltate, hexafluoroferrate (III),tetrachloroferrate(III) or/and tetrachloropalladate(II). Preferredpseudohalides are cyanide, thiocyanate, cyanate, isocyanate andisothiocyanate. Neutral or electron-donor ligands suitable as additionalligands can be, for example, amines, imines, phosphines, phosphites,carbonyl compounds, alkenyl compounds (e.g., allyl compounds), carboxylcompounds, nitriles, alcohols, ethers, thiols or thioethers. Still othersuitable ligands can be carbene ligands such as the diaminocarbeneligands (e.g., N-heterocyclic carbenes).

While the present invention describes a variety of transition metalcomplexes useful in catalyzing organic reactions, one of skill in theart will appreciate that many of the complexes can be formed in situ.Accordingly, ligands (either carbene ligands or additional ligands) canbe added to a reaction solution as a separate compound, or can becomplexed to the metal center to form a metal-ligand complex prior toits introduction into the reaction solution. The additional ligands aretypically compounds added to the reaction solution which can bind to thecatalytic metal center. In some preferred embodiments, the additionalligand is a chelating ligand. While the additional ligands can providestability to the catalytic transition metal complex, they may alsosuppress unwanted side reactions as well as enhance the rate andefficiency of the desired processes. Still further, in some embodiments,the additional ligands can prevent precipitation of the catalytictransition metal. Although the present invention does not require theformation of a metal-additional ligand complex, such complexes have beenshown to be consistent with the postulate that they are intermediates inthese reactions and it has been observed the selection of the additionalligand has an affect on the course of the reaction.

In related embodiments, the present invention provides metal complexes,of the type described above, in which the ligand having Formula I, II,or III has a pendent functionalized side chain (e.g., aminoalkyl,mercaptoalkyl, acyloxyalkyl and the like) in which the functional groupacts as a ligand to provide a bidentate ligand feature. In still otherembodiments, the ligand forms a metal complex with bidentate ligandsthat are not tethered to the cyclic carbene moiety.

In some embodiments, the present invention provides a reaction mixtureincluding a coordination complex including a metal atom and at least oneligand selected from a compound or complex having Formula I, II, or IIIunder conditions sufficient for catalysis to occur, a solvent and anolefin substrate, wherein said olefin substrate is selected toparticipate in an olefin metathesis reaction. In some other embodiments,the olefin substrate is selected as a substrate for ring closingmetathesis. In some embodiments, the olefin substrate is selected as asubstrate for ring opening polymerization metathesis. In some otherembodiments, the olefin substrate is selected as a substrate for crossmetathesis. In some embodiments, the olefin substrate is selected as asubstrate for acyclic diene polymerization metathesis.

V. Catalytic Reactions Suitable for Use with the Compounds and Complexesof the Present Invention

As noted above, the compounds and complexes of the present invention areuseful in catalyzing a variety of organic reactions. The compounds andcomplexes of the present invention include neutral tricoordinate boronderivatives, which act as a Lewis base, and undergoes one-electronoxidation into the corresponding radical cation. Accordingly, thecompounds and complexes of the present invention are useful forcatalyzing Lewis base catalyzed reactions.

The reactions of the present invention can be performed under a widerange of conditions, and the solvents and temperature ranges recitedherein should not be considered limiting. In general, it is desirablefor the reactions to be run using mild conditions which will notadversely affect the reactants, the catalyst, or the product. Forexample, the reaction temperature influences the speed of the reaction,as well as the stability of the reactants and catalyst. The reactionswill typically be run at temperatures in the range of 25° C. to 300° C.,more preferably in the range 25° C. to 150° C.

Additionally, the reactions are generally carried out in a liquidreaction medium, but in some instances can be run without addition ofsolvent. For those reactions conducted in solvent, an inert solvent ispreferred, particularly one in which the reaction ingredients, includingthe catalyst, are substantially soluble. Suitable solvents includeethers such as diethyl ether, 1,2-dimethoxyethane, diglyme, t-butylmethyl ether, tetrahydrofuran and the like; halogenated solvents such aschloroform, dichloromethane, dichloroethane, chlorobenzene, and thelike; aliphatic or aromatic hydrocarbon solvents such as benzene,xylene, toluene, hexane, pentane and the like; esters and ketones suchas ethyl acetate, acetone, and 2-butanone; polar aprotic solvents suchas acetonitrile, dimethylsulfoxide, dimethylformamide and the like; orcombinations of two or more solvents.

In some embodiments, reactions utilizing the catalytic complexes of thepresent invention can be run in a biphasic mixture of solvents, in anemulsion or suspension, or in a lipid vesicle or bilayer. In certainembodiments, the catalyzed reactions can be run in the solid phase withone of the reactants tethered or anchored to a solid support.

In certain embodiments it is preferable to perform the reactions underan inert atmosphere of a gas such as nitrogen or argon.

The reaction processes of the present invention can be conducted incontinuous, semi-continuous or batch fashion and may involve a liquidrecycle operation as desired. The processes of this invention arepreferably conducted in batch fashion. Likewise, the manner or order ofaddition of the reaction ingredients, catalyst and solvent are also notgenerally critical to the success of the reaction, and may beaccomplished in any conventional fashion.

The reaction can be conducted in a single reaction zone or in aplurality of reaction zones, in series or in parallel or it may beconducted batchwise or continuously in an elongated tubular zone orseries of such zones. The materials of construction employed should beinert to the starting materials during the reaction and the fabricationof the equipment should be able to withstand the reaction temperaturesand pressures. Means to introduce and/or adjust the quantity of startingmaterials or ingredients introduced batchwise or continuously into thereaction zone during the course of the reaction can be convenientlyutilized in the processes especially to maintain the desired molar ratioof the starting materials. The reaction steps may be effected by theincremental addition of one of the starting materials to the other.Also, the reaction steps can be combined by the joint addition of thestarting materials to the metal catalyst. When complete conversion isnot desired or not obtainable, the starting materials can be separatedfrom the product and then recycled back into the reaction zone.

The processes may be conducted in either glass lined, stainless steel orsimilar type reaction equipment. The reaction zone may be fitted withone or more internal and/or external heat exchanger(s) in order tocontrol undue temperature fluctuations, or to prevent any possible“runaway” reaction temperatures.

Furthermore, one or more of the reactants can be immobilized orincorporated into a polymer or other insoluble matrix by, for example,derivativation with one or more of substituents of the aryl group.

VI. Methods of Making the Compounds and Complexes of the PresentInvention

In order to be able to protect the boron center while still having spacefor coordination of two carbenes, CAAC 1 (V. Lavallo et al., Angew.Chem. Int. Ed., 44, 5705 (2005)), a ligand featuring a bulky2,6-diisopropylphenyl group at nitrogen and a flexible cyclohexyl moietyas the second carbene substituent was employed (FIG. 1). The first CAACwas installed classically (Y. Wang et al., J. Am. Chem. Soc., 129, 12412(2007); Y. Wang et al., J. Am. Chem. Soc., 130, 3298 (2008); P.Bissinger et al., Angew. Chem. Int. Ed., 50, 4704 (2011)) by reaction of1 with BBr₃ in hexane, which afforded the (CAAC)BBr₃ adduct 2 in 94%.Then, in order to observe the putative (CAAC)BH adduct by a second CAAC,a five-fold excess of potassium graphite was added to 1/1 mixture ofboron adduct 2 and CAAC 1 in dry toluene. The reaction mixture wasstirred at room temperature for 14 hours, and from a complex mixture ofproducts, compound 3 was isolated as a red powder in only 8% yield (FIG.2). Surprisingly, when the same experiment was carried out in theabsence of CAAC 1, the (CAAC)₂BH adduct 3 was also formed, and isolatedin 33% yield. The ¹H-decoupled ¹¹B NMR spectrum of 3 demonstrates abroad signal at 12.5 ppm with a half-width of 216 Hz. In theproton-coupled ¹¹B NMR spectrum, no clear splitting but a broadening ofthe signal with a half-width of 261 Hz was observed. The presence of thehydrogen atom at boron was confirmed by an infrared absorption at 2455cm⁻¹ (FIG. 5), which can be assigned to the B—H stretching mode.Additional experiments demonstrated that the hydrogen atom is abstractedfrom an aryl group of a carbene.

In some embodiments, the present invention provides a method ofpreparing a stable tricoordinate boron in the +1 oxidative state bystabilizing a borylene center with a pair of carbene ligands. The methodincludes contacting a boron trihalide with a pair of carbene ligands ina hexane to form a solution. The method also includes warming thesolution to room temperature with stirring for about 14 hours. Themethod also includes removing the solvent under vacuum to form a productI. Further, the method includes contacting the product I with KC₈ intoluene with stirring for about 14 hours to form a product II. Themethods also includes filtering the KC₈ from the remainder of theproduct II. The methods includes removing the solvent from the productII, drying the product II under vacuum, and washing the product II withpentane to form a product III.

In other embodiments, the present invention provides a methods as setforth herein further including adding the product III to toluene. Themethods also includes contacting the product III in toluene with galliumtrichloride with stirring for about 14 hours. The methods furtherincludes removing the volatiles under vacuum. The methods also includeextracting the solid residue with acetonitrile. The methods includesremoving the solvent under vacuum and drying the solid residue undervacuum.

In some other embodiments, the present invention provides a methods asset forth herein further including contacting trifluoromethanesulfonicacid at room temperature in toluene with product III with stirring forabout 14 hours. The method also includes removing volatiles undervacuum.

In any of the methods set forth herein, the contacting a boron trihalidewith a pair of carbene ligands in a hexane may occur at −78° C. In otherembodiments, the boron trihalide is BBr₃ or BCl₃. In still otherembodiments, the boron trihalide is BBr₃. In other embodiments, the pairof carbene ligands are independent of each other a cyclic(alkyl)(amino)carbene. In certain embodiments, the cyclic(alkyl)(amino)carbene has the following structure:

In yet other embodiments, the present invention provides a tricoordinateboron complex prepared in accordance with any of the methods set forthherein.

VII. Examples

Manipulations were performed under an atmosphere of dry argon usingstandard Schlenk techniques. Solvents were dried by standard methods anddistilled under argon. ¹¹B, and ¹³C NMR spectra were recorded on VarianInova 500 and Bruker 300 spectrometers at 25° C. NMR multiplicities areabbreviated as follows: s=singlet, d=doublet, t=triplet, sept=septet,m=multiplet, br=broad signal. Melting points were measured with a Buchimelting point apparatus system. EPR spectra were recorded on Bruker EMXat 298 K.

Crystallization of Complex of Formula I.

Single crystals suitable for an X-ray diffraction study were obtained byrecrystallization from a dry tetrahydrofuran solution at roomtemperature. In the solid state (FIG. 3, left), the carbene carbons C1and C2, boron, and the hydrogen H1 are in a perfectly planar arrangement(sum of the bond angles at B: 359.94). The B1-C1 [1.5175(15) Å] andB1-C2 [1.5165(15) Å] bond distances are equal and are halfway betweentypical B—C single (1.59 Å) and double (1.44 Å) bonds (M. M. Olmstead,P. P. Power, K. J. Weese, J. Am. Chem. Soc., 109, 2541 (1987)),suggesting the delocalization of the lone pair of electrons at boron tothe empty p-orbitals of the carbene centers. Ab initio calculationsperformed on 3 at the BP86/def2-SVP level of theory support this bondinganalysis. The carbene→BH donation occurs from the a lone pairs ofcarbene ligands into the empty in-plane molecular orbital at boron,affording two low-lying orbitals. The HOMO of 3 (−3.34 eV) isessentially an electron lone pair in the p(n)-orbital of boron, whichmixes in a bonding fashion with the p(π) atomic orbital of the twocarbene carbons (FIG. 4, left). The charge exchange via a donation and πbackdonation leaves the BH moiety in 3 with a partial charge of +0.05 e.For comparison, the BH fragment in (CH₃)₂BH, which has two B—Celectron-sharing bonds, carries a positive charge of +0.61 e. Therefore,the zwitterionic form 3b, featuring a dianionic boron center (J. Monotet al., Angew. Chem. Int. Ed., 49, 9166 (2010)), is a far weakerresonance contributor than 3a, which shows the parent borylenecoordinated by two carbene ligands.

A single crystal X-ray diffraction study showed that the boron center of[3⁺.]GaCl₄ ⁻ is in a perfectly planar arrangement, as observed for itsprecursor 3 (FIG. 3, center). However, the boron-carbon andcarbon-nitrogen bond distances are longer and shorter, respectively,than those of 3, in line with the weaker electron-donation from boron tothe carbene ligand. Compound [3⁺.]GaCl₄ ⁻ is one of very fewcrystallographically characterized boron radicals (M. M. Olmstead, P. P.Power, J. Am. Chem. Soc., 108, 4235 (1986)) and molecules featuringboron in the formal +2 oxidation state (R. Dinda et al., Angew. Chem.Int. Ed., 46, 9110 (2007)).

Cyclic Voltammogram of Complexes of Formulas I, II, or III.

The boron in compound 3 is in the formal oxidation state +1 and iselectron-rich. This was confirmed by the cyclic voltammogram (FIG. 6) ofa THF solution of 3 [0.1 M nBu₄NPF₆ electrolyte], which shows areversible one-electron oxidation at E_(1/2)=−0.940 V versus Fc+/Fc [Fc:ferrocene]. Indeed, addition at room temperature of two equivalents ofgallium trichloride to a toluene solution of 3 quantitatively affordedthe radical cation [3⁺.]GaCl₄ ⁻. The room temperature electronparamagnetic resonance spectrum in THF solution displays a complexsystem (g=2.0026) due to the couplings with the boron [a(¹¹B)=6.432 G],hydrogen [a(¹H)=11.447 G], and two nitrogen nuclei [a(¹⁴N)=4.470 G](FIG. 7). The values of spin couplings with the ¹¹B and ¹H nuclei aresimilar to those observed in the persistent (NHC)BH₂ radical, whereasthe coupling constant with the ¹⁴N nuclei is greater than those in theNHC adducts (T. Matsumoto, F. P. Gabbaï, Organometallics, 28, 4252(2009); J. C. Walton et al., J. Am. Chem. Soc., 132, 2350 (2010)), inline with the higher electron-acceptor ability of CAACs versus NHCs.Calculations using the natural bond orbital (NBO) method, confirmed thatthe spin density is mainly located at boron (0.50 e) with somecontributions of the nitrogen atoms (0.16 e and 0.17 e). The singlyoccupied molecular orbital (SOMO) (−7.30 eV) is essentially the boronp-orbital, weakly mixing with the p(n) atomic orbital of the two carbenecarbons (FIG. 4, right).

Acidity and Basicity Studies

Because of the presence of a lone pair of electrons at boron,bis(carbene)BH adduct 3 can react with electrophiles, which is quiteunusual for tricoordinate boron compounds (Y. Segawa, M. Yamashita, K.Nozaki, Science, 314, 113 (2006); T. B. Marder, Science, 314, 69 (2006);H. Braunschweig, Angew. Chem. Int. Ed., 46, 1946 (2007); K. Nozaki,Nature, 464, 1136 (2010); M. S. Cheung, T. B. Marder, Z. Lin,Organometallics, doi:10.1021/om200115y; H. Braunschweig et al., Angew.Chem. Int. Ed., 49, 2041 (2010)). No reactions of 3 were observed withtrimethylsilyl- or methyl-trifluoromethanesulfonate even after heatingat 80° C. for 14 hours, probably due to the presence of the two bulkyCAAC ligands, which shield the boron center. To probe basicity further,an equimolar amount of trifluoromethane sulfonic acid was added to atoluene solution of compound 3 at room temperature, and after work up,the conjugate acid [3H⁺]CF₃SO₃ ⁻ was isolated in 89% yield. Theproton-coupled ¹¹B NMR spectrum of this salt shows a triplet(J_(BH)=83.5 Hz) at −21.8 ppm, confirming the presence of two hydrogenatoms directly bonded to boron, and thus the boronium nature (W. E.Piers, S. C. Bourke, K. D. Conroy, Angew. Chem. Int. Ed., 44, 5016(2005)) of [3H⁺]CF₃SO₃ ⁻. The solid state structure confirmed thetetracoordination of boron. The boron-carbon and carbon-nitrogen bonddistances are in the range of single and double bonds, respectively, inline with the absence of back-donation from boron to the carbene ligand.To quantify the basicity of 3, the gas phase proton affinity wascalculated (BP86/def2-SVP+ZPE): the 1108 kJ/mol value is much higherthan that calculated for the free BH (856 kJ/mol), and comparable to theunsaturated free N-phenyl substituted NHC (1107 kJ/mol) (R. Tonner, G.Heydenrych, G. Frenking, Chem. Phys. Chem., 9, 1474 (2008)). In toluenesolution, we found that 3 is readily protonated by BrCH₂CO₂H, whereasthe reaction with PhCO₂H proceeded very slowly, and only trace amountsof [3H⁺]PhCO₂ ⁻ were detected after 14 hours. Boronium [3H⁺]CF₃SO₃ ⁻ israpidly deprotonated by sodium ethoxide in a THF solution giving back 3in 68% yield, though no reaction was observed with strong but bulkybases such as potassium hexamethyldisilazide, lithium diisopropylamide,or t-butyllithium, confirming the steric shielding of the boron center(Unsuccessful attempts to deprotonate bis(phosphine)BHX adducts (X: H,Br) were reported by M. Sigl, A. Schier, H. Schmidbaur, Chem. Ber., 130,1411 (1997)).

Stability Studies

Although the parent borylene adduct 3 and the radical cation [3⁺.]GaCl₄⁻ are sensitive to air, they are stable at room temperature under argonboth in solution and in the solid state for two months at least (m.p. 3:328° C.; [3⁺.]GaCl₄ ⁻: 278° C.), which strikingly demonstrates thestabilizing efficiency of CAACs. In marked contrast to the well-knowntricoordinate boron(+3) derivatives, compound 3, featuring a boron inthe +1 oxidation state, behaves as a Lewis base, and can readily beoxidized. Its reactivity with electrophiles is hampered by the bulkinessof the CAAC ligands, but the steric and electronic properties ofcarbenes can be substantially modulated. Compounds of type 3 areisoelectronic with amines and phosphines, and because of the lowerelectronegativity of boron, compared to those of nitrogen andphosphorus, they are potential strong electron-donor ligands fortransition metals.

Synthesis of (CAAC)BBr₃ Adduct 2.

Boron tribromide (5.00 g, 20.0 mmol) was added at −78° C. to a hexanesolution (200 mL) of CAAC 1 (6.50 g, 20.0 mmol). The reaction mixturewas warmed to room temperature and stirred for 14 hours. After thesolvent was removed under vacuum, the resulting white solid was washedwith pentane, and dried under vacuum to give 2 as a white powder (10.80g, 94% yield). ¹H NMR (300 MHz, CDCl₃): δ=7.43 (t, ³J=7.8 Hz, 1H, p-CH),7.25 (d, ³J=7.0 Hz, 4H, m-CH), 3.32-3.16 (m, 2H, CH₂), 2.80 (sept,³J=6.5 Hz, 2H, CH(CH₃)₂), 2.32 (s, 2H, CH₂), 1.98-1.60 (m, 8H, CH₂),1.47 (s, 6H, CH₃), 1.41 (d, ³J=6.5 Hz, 6H, CH(CH₃)₂), 1.30 (d, ³J=6.5Hz, 6H, CH(CH₃)₂); ¹³C NMR (75 MHz, CDCl₃): δ=145.8 (o), 130.4 (p),125.6 (m), 125.2 (ipso), 80.9 (C^(q)), 61.3 (C^(q)), 45.2 (CH₂), 36.9(CH₂), 29.7 (CH₃), 29.5 (CH), 26.5 (CH₃), 25.2 (CH₃), 24.7 (CH₂), 23.1(CH₂); ¹¹B NMR (96 MHz, CDCl₃): δ=−13.5.

Synthesis of bis(CAAC)BH Adduct 3.

Toluene (20 mL) was added at room temperature to a mixture of 2 (1.00 g,1.74 mmol) and potassium graphite (1.17 g, 8.68 mmol). After stirringfor 14 hours, toluene (75 mL) was added to the mixture, and thengraphite and KBr were filtered off. After the solvent was removed undervacuum, the solid residue was washed with pentane (100 mL), and driedunder vacuum to afford 3 as a red powder (185 mg, 33% yield). Singlecrystals of 3 were obtained by recrystallization from a THF solution atroom temperature. Mp: 328° C. (dec.); IR (solid, cm⁻¹) v_(max) 2455(B—H), ¹H NMR (500 MHz, toluene-d₈): δ=7.07-6.92 (m, 6H, m-CH and p-CH),3.34-3.26 (m, 2H, CH₂), 3.09 (sept, ³J=8.3 Hz, 2H, CH(CH₃)₂), 2.75(sept, ³J=8.3 Hz, 2H, CH(CH₃)₂), 2.60-2.53 (m, 2H, CH₂), 2.13 (s, 2H,CH₂), 2.12 (s, 2H, CH₂), 1.87-1.54 (m, 16H, CH₂), 1.30 (d, ³J=8.3 Hz,6H, CH(CH₃)₂), 1.27 (d, ³J=8.3 Hz, 6H, CH(CH₃)₂), 1.19 (d, ³J=8.3 Hz,6H, CH(CH₃)₂), 1.01 (s, 6H, CH₃), 0.99 (s, 6H, CH₃), 0.23 (d, ³J=8.3 Hz,6H, CH(CH₃)₂); attempts to observe the BH signal by 2D ¹¹B-¹H NMR bothin solution and in solid state failed, possibly because of the largequadripolar moment of boron; ¹³C NMR (125 MHz, THF-d_(s)): δ=149.3 (o),147.9 (o), 138.3 (ipso), 127.2 (p), 125.6 (m), 124.4 (m), 68.0 (C^(q)),51.8 (C^(q)), 43.2 (CH₂), 36.4 (CH₂), 31.7 (CH₂), 30.0 (CH₃), 29.5 (CH),29.0 (CH₃), 28.2 (CH), 27.0 (CH₃), 25.4 (CH₃), 24.6 (CH₃), 24.4 (CH₃),24.2 (CH₂×₂), 24.0 (CH₂); ¹¹B NMR (96 MHz, toluene-d₈): δ=12.5(h_(1/2)=216 Hz). ERMS (ESI): 662.5708 [(M)⁺, 662.5713 (C₄₆H₇₁BN₂)].

Synthesis of Radical Cation [3+.]GaCl4-.

Toluene (6 mL) was added at room temperature to a mixture of 3 (150 mg,0.23 mmol) and gallium trichloride (81 mg, 0.46 mmol). After stirringfor 14 hours, volatiles were removed under vacuum. The solid residue wasextracted with acetonitrile (10 mL), then the solvent was removed undervacuum, and the solid residue dried under vacuum to afford [3⁺.]GaCl₄ ⁻as a purple powder (177 mg, 88% yield). Single crystals of [3⁺.]GaCl₄ ⁻were obtained by recrystallization from a mixture of THF and toluene(4:1) solution at room temperature. Mp: 278° C. (dec.). HRMS (ESI):662.5734 [(M)⁺, 662.5713 (C₄₆H₇₁BN₂)]

Synthesis of Boronium [3H⁺]CF₃SO₃ ⁻.

Trifluoromethanesulfonic acid (45 mg, 0.30 mmol) was added at roomtemperature to a toluene (12 mL) solution of 3 (200 mg, 0.30 mmol).After stirring for 14 hours, volatiles were removed under vacuum toafford [3H⁺]CF₃SO₃ ⁻ as a purple powder (217 mg, 89% yield). Singlecrystals of [3H⁺]CF₃SO₃ ⁻ were obtained by recrystallization from a THFsolution at room temperature. [3H⁺]CF₃SO₃ ⁻ decomposes at 246° C.without melting; ¹H NMR (500 MHz, CD₃CN): δ=7.07-7.03 (m, 4H, m-CH),6.89-6.87 (m, 2H, p-CH), 2.83-2.77 (m, 2H, CH₂), 2.40 (sept, ³J=8.3 Hz,2H, CH(CH₃)₂), 2.36 (s, 2H, CHH), 1.98-1.91 (m, 2H, CH₂), 2.00 (s, 2H,CHH), 1.99-1.91 (m, 2H, CH₂), 1.86 (sept, ³J=8.3 Hz, 2H, CH(CH₃)₂),1.77-1.41 (m, 16H, CH₂), 1.18 (s, 6H, CH₃), 1.07 (d, ³J=8.3 Hz, 6H,CH(CH₃)₂), 0.91 (d, ³J=8.3 Hz, 6H, CH(CH₃)₂), 0.87 (s, 6H, CH3), −0.11(d, ³J=8.3 Hz, 6H, CH(CH₃)₂), BH was not found; ¹³C NMR (125 MHz,CD₃CN): δ=145.9 (o), 143.7 (o), 133.9 (ipso), 130.3 (p), 126.69 (m),126.66 (m), 79.9 (C^(q)), 58.1 (C^(q)), 47.3 (CH₂), 36.6 (CH₂), 31.7(CH₂), 30.4 (CH₃), 30.0 (CH), 29.9 (CH₃), 29.5 (CH), 27.4 (CH₃), 26.3(CH₃), 24.6 (CH₃), 24.4 (CH₃), 24.2 (CH₂), 22.4 (CH₂), 22.2 (CH₂); ¹¹BNMR (96 MHz, THF-d_(g)): δ=−21.8 (t, ¹J_(BH)=83.5 Hz, BH₂); ¹⁹F NMR (282MHz, CD₃CN) δ=−80.9; HRMS (ESI): 663.5791 [(M+H)⁺, 663.5791(C₄₆H₇₂BN₂)].

Deprotonation of Boronium [3H⁺]CF₃SO₃ ⁻ with NaOEt.

THF (8 mL) was added at room temperature to a mixture of [3H⁺]CF₃SO₃ ⁻(100 mg, 0.12 mmol) and sodium ethoxide (10 mg, 0.15 mmol). Afterstirring for 14 hours, volatiles were removed under vacuum, and thentoluene (12 mL) was added to the residue. NaOTf was filtered off, thesolvent was removed under vacuum, and the solid residue dried undervacuum to afford 3 (54 mg, 68% yield).

Crystal Structure Determination for Compounds 3, [3+.]GaCl4-, and[3H+]CF3SO3-

The Bruker X8-APEX X-ray diffreaction instrument with Mo-radiation wasused for data collection of compounds 3, [3⁺.]GaCl₄ ⁻, and [3H⁺]CF₃SO₃⁻. All data frames were collected at low temperatures (T=95 and 100 K)using an ω, φ-scan mode (0.3° (ω-scan width, hemisphere of reflections)and integrated using a Bruker SAINTPLUS software package. The intensitydata were corrected for Lorentzian polarization. Absorption correctionswere performed using the SADABS program. The SIR97 was used for directmethods of phase determination, and Bruker SHELXTL software package forstructure refinement and difference Fourier maps. Atomic coordinates,isotropic and anisotropic displacement parameters of all thenon-hydrogen atoms of three compounds were refined by means of a fullmatrix least-squares procedure on F₂. All H-atoms were included in therefinement in calculated positions riding on the C atoms, with U[iso]fixed at 20% higher than isotropic parameters of carbons atoms whichthey were attached. Drawings of molecules were performed using Ortep 3and POVRay for Windows.

Metrical data for the solid state structure of 3, [3⁺.]GaCl₄ ⁻, and[3H⁺]CF₃SO₃ ⁻ are available free of charge from the CambridgeCrystallographic Data Centre under reference numbers CCDC-822247,CCDC-822248, and CCDC-822249, respectively.

TABLE 1 Crystallographic Data and Summary of Data Collection andStructure Refinement. 3 [3^(+.)]GaCl₄ ⁻ [3H+]CF₃SO₃ ⁻ (thf) FormulaC₄₆H₇₁BN₂ C₄₆H₇₁BC1₄GaN₂ C₅₄H₈₀BF₃N₂O₄S Fw 662.86 874.38 885.04 crystsyst Triclinic Orthorhombic Triclinic space group P-1 Pbca P-1 Size(mm³) 0.32 × 0.17 × 0.10 0.30 × 0.15 × 0.10 0.28 × 0.16 × 0.11 T, K   95(2)   100(2)   100(2) a, Å 9.7734(5) 18.572(4) 9.1737(3) b, Å11.1866(6)  17.687(4) 12.1411(4)  C, Å 19.8762(11) 29.302(7) 22.2368(7) α, deg 99.287(3) 90.000 77.971(2) β, deg 93.936(3) 90.000 80.416(2) γ,deg 110.830(3)  90.000 86.380(2) V, A³ 1985.63(18)  9625(4) 2387.48(13)Z 2 8 2 d_(calcd) g · cm⁻³ 1.109 1.207 1.231 μ, mm⁻¹ 0.062 0.825 0.126Refl collected 31039 49691 11833 N_(measd) 12701 13930 9947 [R_(int)][0.0463] [0.0504] [0.0400] R[I > 2sigma(I)] 0.0552 0.0435 0.0713R_(w)[I > 2sigma(I)] 0.1613 0.1231 0.1806 GOF 1.012 1.056 1.192 Largestdiff 0.587/−0.334 0.924/−0.523 0.859/−0.382 peak/hole[e−Å⁻³]

Computational Details

FIG. 8 below shows schematically the bonding situation in (BH)(CAAC)₂ 3.The carbine→BH donation occurs from the σ lone pair of the carbeneligands into the empty in-plane sp and p molecular orbitals at boron.The totally symmetric (+) combination of the r lone pairs donates chargeinto the empty sp(σ) orbital of BH, while the antisymmetric (+ −)combination donates charge into the vacant in-plane p(π) molecularorbital of boron. Thus, the electronic reference state of the BHfragment in (CAAC)₂BH 3 is not the X¹Σ⁺ ground state as in the freeborylene BH, which has a doubly occupied sp(∝) orbital, but it is theexcited C¹Δ state with a p(π) lone-pair (39). The (CAAC)→(BH)←(CAAC) σdonation is complemented by π backdonation from the p(π) lone-pairorbital of BH, which mixes in a bonding fashion with the p(π) atomicorbital of the two carbene carbons, yielding the energeticallyhigh-lying HOMO of 3 (−3.34 eV). The boron-carbon bonds in 3 are ratherstrong. The calculations at BP86/def2-SVP predict a bond dissociationenergy (BDE) for the reaction 3→(X¹Σ⁺) BH+2 CAAC a value of D_(o)=665kJ/mol which gives a mean BDE of D_(o)=332.5 kJ/mol for each C→Bdonor-acceptor bond. This may be compared with the calculated BDE forthe carbon-boron bond in the complex NHC(BH₃) which is only D_(o)=245kJ/mol.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, one of skill in the art will appreciate that certainchanges and modifications may be practiced within the scope of theappended claims. In addition, each reference provided herein isincorporated by reference in its entirety to the same extent as if eachreference was individually incorporated by reference. Where a conflictexists between the instant application and a reference provided herein,the instant application shall dominate.

What is claimed is:
 1. A tricoordinate borylene complex, having thefollowing structure:

wherein R¹ and R² are independently selected from the group consistingof alkyl, aryl, arylalkyl, cycloalkyl, cycloalkylalkyl, heteroaryl,heteroarylalkyl, heterocycloalkyl, and heterocycloalkylalkyl; whereinR⁷, R⁸, R⁹, and R¹⁰ are independently selected from the group consistingof hydrogen, alkyl, aryl, arylalkyl, cycloalkyl, cycloalkylalkyl,heteroaryl, heteroarylalkyl, heterocycloalkyl, andheterocycloalkylalkyl; wherein at least one of R⁷ and R⁸ is other thanhydrogen; wherein at least one of R⁹ and R¹⁰ is other than hydrogen;wherein R³, R⁴, R⁵, R⁶, R¹¹, R¹², R¹³, and R¹⁴ are independentlyselected from the group consisting of hydrogen, acyl, alkyl, alkoxy,amino, aryl, arylalkyl cyano, cycloalkyl, cycloalkylalkyl, halo,heteroaryl, heteroarylalkyl, heterocycloalkyl, heterocycloalkylalkyl,hydroxyl, and nitro; and wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹,R¹⁰, R¹¹, R¹², R¹³, and R¹⁴ are independently optionally substitutedwith 1-5 substituents selected from the group consisting of alkyl,alkoxy, amino, aryl, cycloalkyl, halo, heteroaryl, hydroxyl, and nitro;or a salt, hydrate, or isomer thereof.
 2. The complex of claim 1, havingthe following structure:

wherein Y¹, Y², Y³, and Y⁴ are independently selected from the groupconsisting of aryl, arylalkyl, cycloalkyl, and cycloalkylalkyl; andwherein Y¹, Y², Y³, and Y⁴ are independently optionally substituted withfrom 1-5 substituents selected from the group consisting of alkyl, aryl,halo, heteroaryl, and hydroxyl.
 3. The complex of claim 2, having thefollowing structure:

wherein R¹⁵, R¹⁶, R¹⁷, R¹⁸, R¹⁹, R²⁰, R²¹, R²², R²³, and R²⁴ areindependently selected from the group consisting of hydrogen, acyl,alkyl, alkoxy, amino, cyano, halo, and nitro.
 4. The complex of claim 3,having the following structure:


5. The complex of claim 2, having the following structure:


6. The complex of claim 5, having the following structure:


7. The complex of claim 6, having the following structure:


8. The complex of claim 7, having the following resonance structure:


9. A stable borinylium radical, having the following structure:

wherein R²¹ and R²² are independently selected from the group consistingof alkyl, aryl, arylalkyl, cycloalkyl, cycloalkylalkyl, heteroaryl,heteroarylalkyl, heterocycloalkyl, and heterocycloalkylalkyl; R²⁷, R²⁸,R²⁹, and R³⁰ are independently selected from the group consisting ofhydrogen, alkyl, aryl, arylalkyl, cycloalkyl, cycloalkylalkyl,heteroaryl, heteroarylalkyl, heterocycloalkyl, andheterocycloalkylalkyl; wherein at least one of R²⁷ and R²⁸ is other thanhydrogen; wherein at least one of R²⁹ and R³⁰ is other than hydrogen;wherein R²³, R²⁴, R²⁵, R²⁶, R³¹, R³², R³³, and R³⁴ are independentlyselected from the group consisting of hydrogen, acyl, alkyl, alkoxy,amino, aryl, arylalkyl, cyano, cycloalkyl, cycloalkylalkyl, halo,heteroaryl, heteroarylalkyl, heterocycloalkyl, heterocycloalkylalkyl,hydroxyl, and nitro; and wherein R²¹, R²², R²³, R²⁴, R²⁵, R²⁶, R²⁷, R²⁸,R²⁹, R³⁰, R³¹, R³², R³³, and R³⁴ are independently optionallysubstituted with 1-5 substituents selected from the group consisting ofalkyl, alkoxy, amino, aryl, cycloalkyl, halo, heteroaryl, hydroxyl, andnitro; or a hydrate or isomer thereof.
 10. The radical of claim 9,having the following structure:

wherein Y²¹, Y²², Y²³, and Y²⁴ are independently selected from the groupconsisting of aryl, arylalkyl, cycloalkyl, and cycloalkylyl; and whereinY²¹, Y²², Y²³, and Y²⁴ are independently optionally substituted withfrom 1-5 substituents selected from the group consisting of alkyl, aryl,halo, heteroaryl, and hydroxyl.
 11. The radical of claim 10, having thefollowing structure:

wherein R⁴⁵, R⁴⁶, R⁴⁷, R⁴⁸, R⁴⁹, R⁵⁰, R⁵¹, R⁵², R⁵³, and R⁵⁴ areindependently selected from the group consisting of hydrogen, halo,acyl, alkyl, alkoxy, amino, cyano, and nitro.
 12. The radical of claim11, having the following structure:


13. The radical of claim 10, having the following structure:


14. The radical of claim 13, having the following structure:


15. The radical of claim 14, having the following structure:


16. The radical of claim 15, having the following resonance structure:


17. A boronium salt, having the following structure:

wherein R⁶¹ and R⁶² are independently selected from the group consistingof alkyl, aryl, arylalkyl, cycloalkyl, cycloalkylalkyl, heteroaryl,heteroarylalkyl, heterocycloalkyl, and heterocycloalkylalkyl; R⁶⁷, R⁶⁸,R⁶⁹, and R⁷⁰ are independently selected from the group consisting ofhydrogen, alkyl, aryl, arylalkyl, cycloalkyl, cycloalkylalkyl,heteroaryl, heteroarylalkyl, heterocycloalkyl, andheterocycloalkylalkyl; wherein at least one of R⁶⁷ and R⁶⁸ is other thanhydrogen; wherein at least one of R⁶⁹ and R⁷⁰ is other than hydrogen;R⁶³, R⁶⁴, R⁶⁵, R⁶⁶, R⁷¹, R⁷², R⁷³, and R⁷⁴ are independently selectedfrom the group consisting of hydrogen, acyl, alkyl, alkoxy, amino, aryl,arylalkyl, cyano, cycloalkyl, cycloalkylalkyl, halo, heteroaryl,heteroarylalkyl, heterocycloalkyl, heterocycloalkylalkyl, hydroxyl, andnitro; and wherein R⁶¹, R⁶², R⁶³, R⁶⁴, R⁶⁵, R⁶⁶, R⁶⁷, R⁶⁸, R⁶⁹, R⁷⁰,R⁷¹, R⁷², R⁷³, and R⁷⁴ are independently optionally substituted with 1-5substituents selected from the group consisting of alkyl, alkoxy, amino,aryl, cycloalkyl, halo, heteroaryl, hydroxyl, and nitro; or a hydrate orisomer thereof.
 18. The salt of claim 17, having the followingstructure:

wherein Y³¹, Y³², Y³³, and Y³⁴ are independently selected from the groupconsisting of aryl, arylalkyl, cycloalkyl, and cycloalkylyl; and whereinY³¹, Y³², Y³³, and Y³⁴ are independently optionally substituted withfrom 1-5 substituents selected from the group consisting of alkyl, aryl,halo, heteroaryl, and hydroxyl.
 19. The salt of claim 18, having thefollowing structure:

wherein R⁸⁵, R⁸⁶, R⁸⁷, R⁸⁸, R⁸⁹, R⁹⁰, R⁹¹, R⁹², R⁹³, and R⁹⁴ areindependently selected from the group consisting of hydrogen, halo,acyl, alkyl, alkoxy, amino, cyano, and nitro.
 20. The salt of claim 19,having the following structure:


21. The salt of claim 18, having the following structure:


22. The salt of claim 21, having the following structure:


23. The salt of claim 22, having the following structure:


24. The salt of claim 23, having the following resonance structure:


25. A transition metal complex comprising a transition metal and acomplex of claim
 1. 26. A transition metal complex of claim 25, whereinthe boron in the complex is in the +1 oxidative state and isisoelectronic with an amine.
 27. A transition metal complex of claim 25,wherein the boron in the complex is in the +1 oxidative state and issubstantially as provided in FIG.
 2. 28. A method of preparing a stabletricoordinate boron in the +1 oxidative state by stabilizing a borylenecenter with a pair of carbene ligands, comprising contacting a borontrihalide with a pair of carbene ligands in a hexane at about −78° C. toform a solution; warming the solution to room temperature with stirringfor about 14 hours; removing the solvent under vacuum to form a productI; contacting the product I with KC₈ in toluene with stirring for about14 hours to form a product II; filtering the KC₈ from the product II;removing the solvent from the product II; drying the product II undervacuum; washing the product II with pentane to form a product III. 29.The method of claim 28, further comprising adding the product III totoluene; contacting the product III in toluene with gallium trichloridewith stirring for about 14 hours; removing the volatiles under vacuum;extracting the solid residue with acetonitrile; removing the solventunder vacuum; and drying the solid residue under vacuum.
 30. The methodof claim 28, further comprising contacting trifluoromethanesulfonic acidat room temperature in toluene with product III with stirring for about14 hours; and removing volatiles under vacuum.
 31. The method of claim28, wherein the boron trihalide is BBr₃ or BCl₃.
 32. The method of claim31, wherein the boron trihalide is BBr₃.
 33. The method of claim 28,wherein said pair of carbene ligands are independent of each other acyclic (alkyl)(amino)carbene.
 34. The method of claim 33, wherein thecyclic (alkyl)(amino)carbene has the following structure:


35. A tricoordinate boron prepared in accordance with claim
 28. 36. Amethod of catalyzing a reaction comprising combining a reactant with thetransition metal complex of any of claim 25, 26, or 27, under conditionssufficient for catalysis to occur.
 37. A neutral tricoordinate boroncompound featuring a lone pair at boron, having the following formula:R¹⁰⁰B(L¹)(L²); wherein R¹⁰⁰ is selected from the group consisting ofhydrogen, alkyl, alkoxy, aryl, arylalkyl, aryloxy, cycloalkyl,cycloalkylalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, andheterocycloalkylalkyl; and wherein L¹ and L² are Lewis bases selectedfrom the group consisting of carbenes, phosphines, and amines; or asalt, hydrate, or isomer thereof.
 38. The compound of claim 37, whereinL¹ and L² are independently selected from CAACs.